A wireless communication system can be briefly classified into a system based on a frequency division duplex (FDD) scheme and a system based on a time division duplex (TDD) scheme. In the FDD scheme, uplink transmission and downlink transmission are achieved by occupying two different frequency bands. In the TDD scheme, uplink transmission and downlink transmission are achieved at different times while occupying the same frequency band. A channel response based on the TDD scheme is reciprocal in practice. This implies that a downlink channel response is almost identical to an uplink channel response in a given frequency domain. Therefore, in a TDD-based wireless communication system, the downlink channel response can be advantageously obtained from the uplink channel response.
In the TDD scheme, a full frequency band is time-divided into uplink transmission and downlink transmission, and thus downlink transmission performed by a base station (BS) and uplink transmission performed by a mobile station (MS) cannot be simultaneously achieved. In a TDD system in which uplink transmission and downlink transmission are divided on a subframe basis, uplink transmission and downlink transmission are performed in different subframes.
A wireless communication system employing a relay station (RS) has recently been developed. The RS is employed for cell coverage extension and transmission capability improvement. A BS provides a service to an MS located in a coverage boundary of the BS via the RS, and thus can obtain an effect of extending the cell coverage. In addition, the RS improves signal transmission reliability between the BS and the MS, thereby improving transmission capacity. The RS may be used when the MS is located within the coverage of the BS and is also located in a shadow area.
It is difficult for the RS to receive data from the BS while simultaneously transmitting data to the MS, and on the contrary, it is difficult for the RS to receive data from the MS while simultaneously transmitting data to the BS. This is because a signal output from a transmitting end of the RS may act as interference to a signal to be received by the RS due to self-interference, and as a result, the signal may be distorted.
Since the RS cannot simultaneously perform data reception from the BS and data transmission to the MS (or data transmission to the BS and data reception from the MS), the TDD system may have low efficiency of resource allocation.
Accordingly, there is a need for a method capable of effectively relaying data by an RS in a TDD-based wireless communication system.